What is a Solar Heat Gain Coefficient?

Solar Heat Gain CoefficientThe solar heat gain coefficient (SHGC) refers to the portion of solar energy that passes through a window, skylight, or door whether it’s directly transmitted or absorbed, and then released into the home as heat. A lower SHGC means a lesser amount of solar heat is transmitted and therefore has a greater shading ability. A product that has a higher coefficient rating is more successful at gathering solar heat throughout the winter months. On the other hand, a product with a lower rating can reduce the burden of cooling more effectively by blocking increased heat from the harsh rays of the sun during summer.

Why is Solar Heat Gain Coefficient So Important?

Today, SHGC plays a very critical role in determining a replacement window’s energy efficiency overall.

While solar heat gain can supply free heat in the cold season, it can also result in overheating during the ‘dog days of summer’. The best way to address solar heat gain using a suitable SHGC will primarily depend on the climate, shading conditions, orientation, and other aspects as well. Energy Star suggests various SHGC values based on the climate. Ultimately, this can save you a great deal of money over time in terms of utility bills.

What Affects Solar Heat Gain?

Solar heat gain is affected by the number of glass panes, glass coatings, and the type of glazing. With regards to glazing, solar heat gain can range anywhere from less than 20 percent for high-reflective glass coatings to more than 80 percent for water-white, uncoated clear glass.

Overall, glazing should ideally have a somewhat high SHGC. Also, it shouldn’t obstruct solar heat gains, if at all possible, particularly regarding the sunnier side of the home. Understanding solar heat gain coefficient ratings as well as the ratings that are more conducive for a certain climate is quite useful for home inspectors who regularly perform energy audits.

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